Metro Manila (CNN Philippines) — Dozens were injured Wednesday when police clashed with protesters outside the United States embassy in downtown Manila.

Some 50 protesters and 30 policemen were hurt, the two groups said.

Around 700 members of the militant group Sandugo, an alliance of Moro and indigenous peoples, and the Bagong Alyansang Makabayan had gathered outside the embassy.

They were there to protest the militarization of indigenous peoples' lands and express support for the independent foreign policy of President Rodrigo Duterte as he began his state visit to China.

Police said protesters lacked a permit to rally and that authorities did not expect violence to ensue.

Those arrested will be charged with malicious mischief, resisting arrest, and violation of Batas Pambansa 880 or the Public Assembly Act of 1985, said Manila Police District deputy director for operations Marcelino Pedroso.

Police have yet to confirm the number of protesters arrested, but Sandugo said 29 of their members were taken into police custody.

Two female minors who were part of a Lumad tribe in Bukidnon, were among those arrested, said the Gabriela Women's Party in a statement.

Tensions flared when some protesters allegedly attacked a police vehicle two meters away from the main entrance of the embassy.

Police then fired tear gas to disperse the crowd, some of whom vandalized the embassy walls with anti-American slogans.

A police vehicle backed up into the crowd, hurting some of the protesters.

When asked about this, Pedroso said the driver may have panicked.

"This is a peaceful protest of our national minorities and this is how the police treat them," Bayan Muna Representative Carlos Isagani Zarate, as he condemned the violence.

Senator Leila de Lima urged Philippine National Police Chief Ronald Dela Rosa to investigate the incident and the use "unnecessary force" to disperse the rallyists.